The invention relates to a method of logging messages sent over a data bus in a motor vehicle between electronic units. Selected critical messages may be temporarily stored and later, at a suitable point in time, transferred into a data processing device externally of the motor vehicle, where such critical messages may be analyzed in more detail.
German Offenlegungsschrift DE 101 21 061 A1discloses a monitoring apparatus and a monitoring system for a data bus which is provided in a motor vehicle and on which messages are sent between electronic units. Several electronic units are connected to the data bus by a bus interface, and the communication network in the motor vehicle has a data interface, by means of which an error memory may be read into a data processing device externally of the motor vehicle. As a difference from the presently claimed invention, however, in the monitoring method according to the DE 101 21 061 A1, the messages on the bus are verified directly by a monitoring unit without temporary storage. The verification is performed with a list which is stored in a memory of the monitoring unit and in which all the permitted messages occurring on the bus are enumerated. In case on the bus a message appears which is not present in such a list, then such a foreign message is submitted to an evaluation, and an evaluating unit signals an endangering potential which may emerge from the foreign message. In case the thus determined endangering potential exceeds a previously given threshold value, an error signal is entered into an error memory. Such a known monitoring system serves for recognizing, whether all connected bus participants also have a corresponding access privilege to the bus. This may cause a problem in motor vehicles if control devices are subsequently installed without a corresponding clearance being available from the vehicle manufacturer for such control devices. In such a case a control device not cleared for installation could not be immediately recognized by the monitoring apparatus according to the DE 101 21 061 A1.
German Patent Application DE 100 46 832 A1describes an apparatus and a method for detecting travel data of a motor vehicle. The travel data are logged in an accident recorder. The latter consists essentially of a memory device which is a continuous memory and whose memory contents are cyclically overwritten. In this manner the recorded data are always preserved for a predetermined time period before they are continuously overwritten by the actual data upon lapse of the predetermined time period. The travel data are directly stored in the accident recorder. A bus monitoring or an analysis of bus messages is not provided, nor is a readout of the accident recorder during normal operation of the motor vehicle.
Possibilities of a bus access during the operational period of a motor vehicle are known from the vehicle management system in German Offenlegungsschrift DE 101 43 556 A1. The control devices in the motor vehicle may be accessed by an air interface, and a telematic-CAN-data bus as well as by a CAN-gateway. The access itself is tied to an access privilege. A monitoring of the bus traffic concerning error events or error messages is not performed.
Bus messages are not logged in any of the above-discussed processes. It is therefore not possible with any of the known methods or with any combination thereof to more closely analyze an error-encumbered bus traffic. This is achieved only by the invention.
The inventors were therefore faced with the object to develop, for further advancement and for the elimination of errors in the existing software of control devices in a motor vehicle, a data capture which assists in tracking down such software errors.